This invention relates to a creep preventing safety device for hydraulic jacks of the type employed for either partially or fully raising road vehicles, but not limited thereto.
Such hydraulically operated jacks comprise in general a strong bearing frame, which carries journalled thereto a lifting arm and a force applying cup positioning linkage, as well as a power lever or tiller and a foot lever for fast no-load elevation of the lift arm. The power lever and foot lever control and/or actuate the power applying hydraulic unit of the jack, which unit is usually mounted between two opposite side plates included in said bearing frame. The hydraulic unit, as is well known, comprises basically a hydraulic cylinder/piston system which operates on a closed circuit differential pumping action principle, the cylinder body being pivoted to the frame, while the piston rod acts on the lifting arm, whereto it is similarly pivoted.
In most applications, and particularly when used for raising parts of a road vehicle, said bearing frame is installed on wheel pairs, one such pairs comprising two strong load bearing wheels, and the other pair comprising in general castor wheels.
In conventional hydraulic jacks of the general type described above, position retention of the lifting arm while loaded is entirely dependent on the detenting capacity of the hydraulic unit, thereby, when one is required to operate in completely safe conditions, the raised vehicle has to be propped up by means of fixed stands or supports.